CVE-2019-11396 in Free Security Suite
Summary
by MITRE
An issue was discovered in Avira Free Security Suite 10. The permissive access rights on the SoftwareUpdater folder (files / folders and configuration) are incompatible with the privileged file manipulation performed by the product. Files can be created that can be used by an unprivileged user to obtain SYSTEM privileges. Arbitrary file creation can be achieved by abusing the SwuConfig.json file creation: an unprivileged user can replace these files by pseudo-symbolic links to arbitrary files. When an update occurs, a privileged service creates a file and sets its access rights, offering write access to the Everyone group in any directory.
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Analysis
by VulDB Data Team • 12/11/2023
The vulnerability identified as CVE-2019-11396 represents a critical privilege escalation flaw within Avira Free Security Suite version 10 that stems from improper access control mechanisms in the SoftwareUpdater component. This issue manifests through the creation of permissive access rights on the SoftwareUpdater folder structure, which includes both files and configuration elements that are typically managed with elevated privileges. The core technical flaw lies in how the security suite handles file creation and access permissions during update operations, creating an exploitable condition where unprivileged users can manipulate the system to gain SYSTEM-level privileges.
The vulnerability operates through a specific attack vector involving the SwuConfig.json file manipulation, which serves as the primary entry point for exploitation. When an unprivileged user can create or replace this configuration file with a pseudo-symbolic link pointing to arbitrary system files, they effectively create a pathway for privilege escalation. This technique leverages the fact that the privileged service responsible for update operations creates files with overly permissive access controls, specifically granting write access to the Everyone group across any directory. This design flaw aligns with CWE-276, which addresses improper file permissions, and represents a classic case of insecure file handling in privileged contexts.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it fundamentally undermines the security model of the affected software suite. An attacker can exploit this condition to execute arbitrary code with SYSTEM privileges, potentially leading to complete system compromise. The vulnerability is particularly concerning because it requires no special privileges to initiate the attack, making it accessible to any user on the system. This type of flaw directly relates to ATT&CK technique T1068, which covers the exploitation of legitimate credentials and system access, and T1059, which covers command and scripting interpreter usage for privilege escalation.
Mitigation strategies for this vulnerability should focus on implementing proper access control mechanisms within the SoftwareUpdater component and addressing the root cause of the overly permissive file creation behavior. System administrators should immediately update to the latest version of Avira Free Security Suite where this vulnerability has been patched, as the vendor has addressed the issue through improved file permission handling and more restrictive access controls. Additionally, implementing principle of least privilege for the SoftwareUpdater service and conducting regular security audits of file access permissions can help prevent similar issues. The vulnerability demonstrates the critical importance of proper privilege separation and access control in security software, as the exploitation of such flaws can provide attackers with complete system compromise through seemingly minor access control oversights.